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AfiRIGULIUBAL 
UIBARY 


UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  236 


GERM  CONTENT  OF  MILK 

III.  AS  INFLUENCED  BY  VISIBLE  DIRT 

BY  H.  A.  HARDING  AND  M.  J.  PRUCHA 


URBANA,  ILLINOIS,  DECEMBER,  1921 


CONTENTS  OF  BULLETIN  No.  236 

PAGE 
INTRODUCTION 363 

HISTORICAL 364 

Methods  of  Determining  Amount  of  Dirt 364 

Sources  of  Dirt  Found  in  Milk 366 

Kinds  of  Dirt  Found  in  Milk 367 

Amount  of  Dirt  Found  in  Milk 369 

EXPERIMENTAL  RESULTS 371 

Plan  of  the  Experiments 371 

Effect  of  Dirt  from  Relatively  Clean  Cows 371 

Effect  of  Dirt  from  Extremely  Dirty  Cows 373 

Plan  of  the  Study 374 

Determining  the  Dirt  in  the  Milk 374 

Series  I— When  the  Small- Topped  Pail  was  Used 375 

Series  II— When  the  Ordinary  Milk  Pail  was  Used 378 

Series  III— When  the  Cows  Had  Been  Cleaned 380 

Discussion  of  the  Results  of  the  Three  Series 382 

Germ  Count  of  Dirt  from  Extremely  Dirty  Cows 384 

SUMMARY  AND  CONCLUSIONS 388 

RELATION  OF  THESE  RESULTS  TO  THE  PROBLEM  OF  CLEAN  MILK. 389 
REFERENCES  .  ..390 


GERM  CONTENT  OF  MILK 

III.  AS  INFLUENCED  BY  VISIBLE  DIRT 

BY  H.  A.  HARDING,  CHIEF  IN  DAIRY  BACTERIOLOGY,  AND 
M.  J.  PEUCHA,  CHIEF  IN  DAIRY  BACTERIOLOGY 

INTRODUCTION 

For  a  number  of  years  attention  has  been  directed  to  the  problem 
of  the  most  economical  production  of  milk  of  high  quality.  A  high 
quality  milk  has  been  defined  as  one  which  is  rich,  safe,  clean,  and 
sweet.1  In  order  that  such  milk  be  most  economically  produced,  it  is 
necessary  that  the  influence  of  each  step  in  the  preparation  of  the  milk 
upon  each  of  these  qualities  be  clearly  understood. 

Because  keeping  quality,  or  the  ability  to  remain  sweet  and  in 
satisfactory  condition,  was  the  element  in  milk  quality  in  which  de- 
ficiencies were  most  evident,  recent  studies  have  been  largely  con- 
cerned with  the  germ  content  of  milk,  since  this  is  the  factor  control- 
ling keeping  quality. 

It  is  a  fundamental  requirement  that  human  food  in  general  and 
milk  in  particular  be  clean.  As  this  statement  expresses  a  funda- 
mental fact,  it  should  not  be  taken  in  a  narrow  or  technical  sense. 
Even  the  finest  certified  milk  contains  a  slight  amount  of  material 
which  under  any  classification  would  be  called  dirt.  However,  the 
amount  of  this  material  is  so  slight  that  such  milk  is  unhesitatingly 
classed  as  clean. 

Because  of  the  common  feeling  that  dirt  spreads  disease,  the  funda- 
mental requirement  of  cleanliness  is  often  confused  with  the  equally 
fundamental  requirement  of  safety.  Since  the  diseases  spread  thru 
milk  are  principally  caused  by  bacteria,  the  bacterial  count  is  some- 
times considered  as  an  index  of  the  cleanliness  and  of  the  safety  of 
the  milk. 

That  a  high  germ  count  in  milk  is  no  indication  of  the  probable 
presence  of  germs  of  tuberculosis,  typhoid  fever,  diphtheria,  or  any 
of  the  other  disease  germs  known  to  be  carried  at  times  by  milk,  would 
probably  be  agreed  to  by  all  students  of  the  question. 

On  the  other  hand,  there  is  difference  of  opinion  as  to  the  extent 
to  which  a  high  germ  count  in  milk  indicates  the  presence  of  dirt. 
This  difference  of  opinion  arises  in  part  because  of  the  differences  in 
what  is  considered  as  dirt  in  milk.  Hair,  dandruff,  particles  of  soil, 
and  all  visible  foreign  matter  in  milk  is  unhesitatingly  classed  as  dirt 
by  all  students,  and  any  portion  of  similar  matter  in  solution  in  the 

363 


364  BULLETIN  No.  236  [December, 

milk  is  also  classed  as  dirt.  There  is,  however,  a  difference  of  opinion 
as  to  whether  the  bacteria  entering  the  milk,  mainly  from  dairy 
utensils,  shall  be  classed  as  dirt. 

All  would  agree  that  bacteria  are  undesirable  in  a  sweet  milk 
supply,  and  that  care  should  be  exercised  to  keep  their  numbers  as 
low  as  practicable.  However,  as  the  presence  of  pathogenic  germs  is 
considered  in  connection  with  the  safety  of  the  milk,  and  the  other 
relations  of  germ  life  to  milk  are  covered  by  keeping  quality,  the  con- 
sideration of  bacteria  as  dirt  serves  no  good  purpose  and  makes  for 
confusion  rather  than  clearness.  Accordingly,  in  the  present  pub- 
lication the  word  dirt  will  be  used  to  designate  the  foreign  matter  in 
milk  which  is  ordinarily  visible,  tho  small  amounts  of  this  material  may 
go  into  solution.  All  gravimetric  determinations  of  the  dirt  found 
in  milk  under  various  dairy  conditions  are  necessarily  restricted  to 
the  insoluble  dirt,  while  the  bacteriological  measurements  of  the  germ 
life  accompanying  such  dirt  includes  the  germ  life  accompanying  the 
soluble  dirt  as  well.  However,  in  the  present  study  the  amount  of 
soluble  dirt  was  too  small  to  be  detected,  and  tests  seemed  to  show 
further  that  there  is  no  appreciable  error  in  attributing  the  germ  life 
found  to  the  visible,  insoluble  dirt. 

The  data  upon  which  this  publication  is  based  were  secured  during 
the  years  1914  to  1917.  Three  former  members  of  this  department 
took  an  active  part  in  the  conduct  of  these  experiments.  The  success 
of  the  bacteriological  work  depended  to  a  large  extent  upon  Messrs. 
H.  M.  Weeter  and  W.  H.  Chambers.  The  problem  of  removing  and 
accurately  determining  the  dirt  present  in  over  3,000  pounds  of  milk 
was  successfully  handled  by  Dr.  E.  F.  Kohmann.  The  efficient  par- 
ticipation of  these  men  in  this  work  is  gratefully  acknowledged. 

HISTORICAL 

Foreign  matter  stands  out  so  distinctly  against  the  white  back- 
ground of  the  milk  itself  that  the  cleanliness  of  milk  has  long  been 
a  matter  of  general  interest.  The  use  of  milk  strainers  or  filters  to 
remove  foreign  particles  is  an  old  and  practically  universal  practice. 
The  observation  that  dirt  was  thrown  out  against  the  walls  of  the 
separator  bowl  led  to  the  development  of  the  modern  mechanical  milk 
clarifier,  which  fairly  completely  removes  insoluble  foreign  matter. 

Modern  milk  production  is  characterized  on  one  hand  by  an  in- 
creasing care  in  keeping  dirt  out  of  milk,  and  on  the  other  hand  by 
improved  mechanical  means  for  removing  the  small  amount  of  foreign 
matter  which  unavoidably  enters  during  the  milking  process. 

METHODS  OF  DETERMINING  AMOUNT  OF  DIRT 

Considering  the  universal  interest  in  this  question  of  dirt  in  milk, 
methods  for  the  measurement  of  the  dirt  are  comparatively  recent. 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIET  365 

in  1891  von  Renk2  pointed  out  that  if  one  liter  (about  one  quart)  of 
milk  was  allowed  to  stand  in  a  tall  vessel,  the  dirt  would  settle,  all 
but  a  small  amount  of  the  milk  could  be  carefully  poured  off,  the 
remainder  diluted,  and  the  process  repeated  until  the  liquid  would 
pass  thru  a  filter  paper.  The  dirt  caught  on  the  paper  could  be  dried 
and  weighed.  This  remains  one  of  the  present  methods  of  determin- 
ing the  dirt  in  milk,  tho  various  modifications  have  been  suggested, 
such  as  changing  the  shape  of  the  sedimenting  chamber,  adding  pre- 
servatives to  prevent  souring,  and  adding  alkalies  to  dissolve  the 
casein  and  facilitate  sedimentation. 

Von  Renk  suggested  that  the  filter  papers  carrying  the  dirt  could 
be  displayed  as  an  argument  for  the  more  careful  handling  of  the 
milk.  This  suggestion  was  a  forerunner  of  the  modern  sediment  test, 
and  the  modern  use  of  the  sediment-test  results. 

The  growing  interest  in  clean  milk  led  to  the  use  of  various  ma- 
terials as  milk  filters,  and  in  1904  Fliegel3  devised  a  filter  consisting 
of  two  perforated  metal  disks  supporting  a  disk  of  cotton.  This  was 
intended  for  collecting  and  weighing  the  dirt  in  a  measured  amount 
of  milk,  and  in  principle  is  practically  identical  with  present  sedi- 
ment testers. 

Bernstein,4  in  1906,  devised  a  similar  apparatus  primarily  for 
commercial  use  and  with  the  idea  of  using  the  resulting  cotton  disks 
in  grading  the  milk  and  in  stimulating  more  care  in  milk  production. 

In  this  country  apparently  the  earliest  suggestion  of  considering 
the  dirt  content  in  modifying  the  price  of  milk  was  made  by  Weld5 
in  1907.  He  used  individual  strainer  cloths  in  collecting  the  dirt.  The 
sediment  tester  which  is  most  commonly  employed  in  America  was  de- 
scribed by  Babcock  and  Farrington  in  1910.°  It  collects  the  dirt  from 
a  pint  of  milk  upon  a  pad  of  cotton. 

The  dirt  caught  on  the  cotton  pad  of  a  sediment  tester  presents  a 
striking  picture  and  early  suggested  the  use  of  such  pads  as  the  basis 
for  grading  milk.  Standards  can  be  readily  prepared  by  the  use  of 
milk  containing  known  amounts  of  impurities,  and  in  this  way  the 
dirt  content  of  the  milk  may  be  quickly  and  accurately  estimated. 
Such  standards  have  been  used  by  the  Chicago  Department  of  Health 
since  1910.7  Similar  standards  for  dividing  milk  into  five  degrees  of 
cleanliness  are  given  in  the  "Standard  Methods  for  the  Sanitary 
Analysis  of  Milk".8 

The  von  Renk  method,  while  fairly  accurate,  requires  considerable 
time  for  the  dirt  to  settle.  In  1898  Eichloff9  suggested  that  time 
could  be  saved  and  more  accurate  results  could  be  obtained  by  sub- 
stituting centrifugal  force  for  .the  force  of  gravity  in  removing  dirt 
from  the  sample  of  milk.  He  whirled  300-cc.  samples  in  specially 
devised  containers  and  obtained  good  results.  Stocking,10  in  carry- 
ing out  one  of  the  first,  if  not  the  first,  study  of  the  dirt  content  of 
milk  under  American  conditions,  modified  this  method  by  passing 


366  BULLETIN  No.  236  [December, 

known  amounts  of  milk  thru  a  centrifugal  separator  and  collecting 
and  weighing  the  dirt  deposited  in  the  separator  bowl. 

It  is  seen  that  three  groups  of  methods  for  determining  the  dirt 
content  of  milk  have  been  devised,  differing  in  that  they  depend  upon 
sedimentation,  nitration,  or  centrifugal  force  as  a  means  of  separat- 
ing the  dirt  from  the  milk.  Each  of  these  methods  has  advantages; 
the  centrifugal  method  is  probably  somewhat  more  accurate ;  the  sedi- 
mentation method  calls  for  less  machinery;  while  the  cotton  filter 
method  is  the  simplest  and  quickest,  and  when  small  amounts  of  dirt 
are  involved,  possesses  a  high  degree  of  accuracy. 

It  will  be  noted  that  all  of  these  methods  of  measuring  dirt  in 
milk  assume  that  this  dirt  is  both  visible  and  insoluble.  Neither  of 
these  assumptions  is  entirely  true.  Practically  all  of  the  dirt  falling 
into  the  milk  is  dry  and  quite  insoluble.  Accordingly,  while  it  should 
not  be  claimed  that  the  sediment  test  or  similar  tests  show  all  of  the 
dirt  in  milk,  the  error  of  measurement  involved  in  such  sediment  tests, 
when  properly  made,  is  undoubtedly  less  than  the  error  involved  in 
the  ordinary  determinations  of  germ  content  of  milk. 

SOURCES  OF  DIRT  FOUND  IN  MILK 

Since  milk  is  regularly  placed  in  covered  cans  within  a  few  minutes 
after  it  is  drawn  from  the  cow,  the  entrance  of  foreign  matter  at  the 
farm  is  restricted  to  these  first  few  minutes,  except  in  the  unusual 
cases  where  the  covers  of  the  cans  are  removed  during  the  cooling 
process.  Before  the  glass  bottle  came  into  general  use,  the  milk  was 
exposed  to  street  dust  at  the  time  of  delivery  to  the  consumer.  At 
present  the  delivery  of  dipped  milk  is  prohibited  by  ordinance  in 
many  cities  and  is  generally  considered  an  undesirable  practice. 

The  Air. — In  the  early  production  of  certified  milk  extreme  atten- 
tion was  given  to  the  dirt  content  of  the  stable  air,  and  in  the  direc- 
tions for  market  milk  production  the  dairyman  has  long  been  urged 
to  avoid  the  feeding  of  hay,  straw,  or  other  dust-producing  feeds  dur- 
ing the  milking  process.11  These  recommendations  and  practices  were 
based  upon  the  fact  that  the  resulting  dust  in  the  air  could  be  easily 
seen,  and  upon  the  belief  that  this  dust  carried  large  amounts  of  germ 
life.  In  the  cases  where  the  amount  of  dirt  in  milk  has  been  deter- 
mined and  found  to  be  relatively  large,  frequently  one-half  or  more 
of  the  total  dirt  consisted  of  particles  of  hay,  straw,  or  chaff.  While 
such  material  is  clearly  objectionable,  and  rarely  finds  its  way  into 
milk  under  proper  stable  management,  it  should  be  remembered  that 
from  the  esthetic  standpoint  this  material  is  fairly  clean  and  is  among 
the  least  offensive  foreign  materials  found  in  milk. 

The  Utensils.— In  Bulletin  204  of  this  Station,12  attention  was 
called  to  the  fact  that  from  a  few  thousand  to  a  million  germs  per 
cubic  centimeter  are  added  to  milk  from  the  utensils,  particularly 


1021}          GERM  CONTENT  OP  MILK  AS  INFLUENCED  BY  VISIBLE  DIRT  367 

from  the  milk  cans.  These  figures  will  lead  many  to  conclude  that 
the  milk  utensils  studied  were  dirty.  Such  was  not  the  case.  A  careful 
examination  of  these  utensils  would  have  shown  them  unusually  free 
from  any  visible  dirt,  with  the  exception  of  a  part  of  the  cans,  and 
these  cans  were  up  to  the  ordinary  standards  of  cleanliness.  Utensils 
classed  as  "dirty"  usually  contain  evident  remnants  of  milk.  Since 
utensils  which  would  ordinarily  be  called  clean  but  which  have  not 
been  thoroly  dried,  exert  such  a  pronounced  effect  upon  the  keeping 
quality  of  milk,  the  effect  of  utensils  in  which  evident  traces  of  milk 
have  remained  and  decomposed  is  so  disastrous  that  the  practice  is 
self-limiting.  Accordingly,  while  dairy  utensils  frequently  leave  much 
to  be  desired  from,  the  standpoint  of  germ  life,"  at  the  time  they  re- 
ceive the  milk  they  are  usually  satisfactorily  free  from  evident  for- 
eign matter.  Because  of  the  mechanical  difficulties  involved  in  wash- 
ing them,  the  milk  cans  are  probably  the  most  frequent  exceptions 
to  this  general  statement. 

It  should  be  noted  in  this  connection  that  the  form  of  milk  pail 
exerts  a  marked  influence  upon  the  amount  of  dirt  falling  into  the 
milk  during  the  act  of  milking.  Stocking13  has  shown  that  milk  drawn 
into  a  small-topped  pail  contained  40  percent  less  dirt  than  when  an 
ordinary  pail  was  used.  Measurements  of  the  effect  of  milking  ma- 
chines upon  the  dirt  content  of  milk  are  still  lacking,  tho  it  seems 
evident  that  when  properly  handled  they  will  largely  prevent  the 
entrance  of  dirt. 

The  Milker. — That  the  milker  who  is  a  disease-germ  carrier  is  an 
element  of  danger  is  well  known.  However,  it  is  certainly  very  rare 
that  any  measurable  amount  of  dirt  from  the  milker  enters  the  milk. 
On  the  other  hand  the  care,  or  lack  of  care,  exercised  by  the  milker 
during  the  milking  process  undoubtedly  exerts  an  influence  upon  the 
amount  of  dirt  finding  its  way  into  the  milk  from  other  sources. 
Exact  measurements  of  the  influence  of  this  factor  upon  the  dirt  con- 
tent are  unfortunately  lacking. 

The  Coat  of  the  Cow. — The  most  important  source  of  dirt  in  milk  is 
the  coat  of  the  cow.  The  amount  of  dirt  coming  from  this  source 
differs  markedly  with  the  season.  The  coat  is  ordinarily  most  dirty 
in  the  winter,  when  the  cows  are  continuously  stabled,  particularly  if 
their  stalls  are  not  dry,  or  if  they  are  not  furnished  with  sufficient 
bedding.  The  coat  is  often  muddy  in  the  spring  and  ordinarily  it  is 
cleanest  in  summer  when  the  cows  spend  practically  all  of  their  time 
in  the  open  air. 

KINDS  OF  DIRT  FOUND  IN  MILK 

While  the  consuming  public  objects  to  any  dirt  in  milk,  some  kinds 
of  dirt  are  much  more  offensive  than  others. 

Dust. — A  beam  of  light  entering  thru  a  small  hole  practically 
always  shows  considerable  dust  in  the  barn  air.  A  study  of  barn 


368  BULLETIN  No.  236  [December, 

dust14  shows  that  it  may  be  divided  into  two  classes:  that  which  is 
so  light  as  to  float  in  the  air,  and  the  remainder  which  settles  promptly. 
The  floating  particles  are  quite  dry  and,  therefore,  are  in  poor  condi- 
tion for  supporting  germ  life.  The  researches  of  Winslow15  indicate 
that  all  but  about  one  such  particle  in  one  thousand  are  sterile.  The 
shape  of  the  cow  is  such  that  during  the  milking  process  she  functions 
like  an  umbrella  in  protecting  the  milk  from  falling  particles,  except 
those  which  fall  from  her  own  body.  Accordingly,  little  of  the  dust 
from  the  barn  air  finds  its  way  into  the  milk  except  in  those  cases 
where  milk  stands  exposed  in  the  barn,  or  in  the  rare  cases  where  it 
is  later  exposed  to  dusty  air. 

Feed. — Objection  is  commonly  raised  to  the  feeding  of  straw,  hay, 
corn  fodder,  or  dry  ground  feeds  during  milking.  For  the  reasons 
already  given,  little  of  this  material  finds  its  way  into  the  milk  unless 
the  open  pails  or  cans  are  allowed  to  stand  in  the  barn,  or  the  milk 
pail  is  used  in  carrying  ground  feed.  Both  of  these  practices  are 
objectionable  and  fortunately  are  rather  infrequent. 

Milk  Remnants. — Improperly  cared  for  utensils  sometimes  contain 
remnants  of  milk.  While  there  may  be  some  difference  of  opinion  as 
to  whether  these  remnants  should  be  classed  as  dirt,  the  germ  life 
accompanying  them  is  objectionable  because  of  its  effect  on  the  keep- 
ing quality  of  the  milk.  This  effect  on  keeping  quality  is  well  under- 
stood, and  the  ordinary  milk  utensils  are  carefully  freed  from  all 
traces  of  old  milk  before  they  are  used.  Unfortunately  the  same  can 
not  always  be  said  of  the  tubes  of  the  milking  machine. 

Very  little  material  from  these  milk  remnants  finds  its  way  into 
the  milk,  except  where  milking  machines  are  used.  Even  here  such 
material  is  rarely  present  in  sufficient  amount  to  be  detected  by  any 
of  the  available  tests  for  dirt,  even  where  the  effect  of  the  germ  life 
upon  the  keeping  quality  is  clearly  evident.  The  fact  that  this  ma- 
terial is  overlooked  in  measurements  of  the  dirt  content  is  largely 
compensated  for  by  the  fact  that  where  it  is  present,  even  in  minute 
quantities,  the  effect  of  its  germ  content  is  noted  in  the  measurements 
of  keeping  quality. 

Hair. — While  the  milking  machine  is  open  to  the  objection  already 
mentioned,  it  largely  prevents  the  introduction  of  the  considerable 
number  of  foreign  particles  which  almost  invariably  enter  during 
hand  milking.  Of  these  particles,  hair  is  fairly  common.  The  amount 
of  hair  falling  into  the  milk  is  quite  variable,  being  especially  abundant 
in  the  spring  when  the  cows  are  shedding  their  winter  coats  (see 
page  376),  but  some  hair  finds  its  way  into  the  milk  at  practically  all 
seasons  of  the  year. 

Dandruff. — Likewise,  dandruff  is  constantly  being  loosened  from 
the  skin  of  the  udder  and  the  adjacent  parts  by  the  act  of  milking, 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIRT  369 

and  it  falls  into  the  milk  pail.  While  constantly  present,  the  total 
amount  of  this  material  is  usually  small. 

Soil. — Whenever  conditions  are  such  that  the  flanks  and  udder  of 
the  cow  become  muddy,  there  is  the  possibility  of  the  dried  mud  or 
soil  finding  its  way  into  the  milk.  Such  cows  are  ordinarily  cleaned 
before  they  are  milked.  However,  in  the  case  of  cows  not  evidently 
dirty,  there  is  frequently  a  small  amount  of  dry  dirt  mechanically 
held  among  the  hairs  of  the  flank  and  udder.  During  the  milking 
process  some  of  this  dirt  may  fall  into  the  milk. 

Manure. — Most  objectionable  of  all  the  dirt  which  finds  its  way 
into  the  milk  is  cow  feces.  From  the  statements  which  are  frequently 
made,  it  might  be  inferred  that  fresh  cow  feces  are  commonly  found 
in  milk.  This  idea  is  entirely  erroneous  and  fresh  feces  find  their 
way  into  milk  so  infrequently,  if  at  all,  that  the  probability  of  their 
presence  can  be  safely  disregarded.  However,  where  the  cows  are 
stabled  without  adequate  bedding,  a  mixture  of  bedding  and  feces 
may  adhere  to  their  flanks.  In  case  this  material  is  not  thoroly  re- 
moved, it  will  become  dry  and  brittle,  and  during  the  milking  process 
some  portions  of  it  may  be  dislodged  and  find  their  way  into  the 
milk.  While  the  amount  of  this  dry  material  thus  entering  the  milk 
even  in  extreme  cases  is  small  where  proper  attention  is  given  to  the 
bedding  and  the  coat  of  the  cow,  such  entrance  commonly  is  and 
should  be  prevented.  It  is  the  just  indignation  over  the  occasional 
finding  of  traces  of  such  material  in  milk  which  has  led  to  exaggerated 
statements  regarding  the  uncleanliness  of  milk  supplies.  The  public 
will  not  be  satisfied  until  the  probability  of  such  material  reaching  the 
milk  is  practically  eliminated. 

AMOUNT  OF  DIRT  FOUND  IN  MILK 

Altho  dirt  from  a  dozen  different  sources  occasionally  finds  its 
way  into  milk,  the  amount  of  each  kind  of  dirt  present  is  usually 
too  small  to  be  determined  separately.  Eemoving  and  weighing  the 
visible,  insoluble  dirt  in  milk  according  to  any  modification  of  the 
von  Renk  method  is  a  slow  and  laborious  process.  Simpler  methods 
are  how  available,  but  thus  far  they  have  apparently  not  been  widely 
applied  to  the  study  of  this  problem.  The  available  data  regarding  the 
dirt  content  of  the  milk  of  various  cities  were  assembled  in  1907  by 
Grosse-Bohle16  and  these  are  shown  in  the  following  table. 

Lowest  Highest                                                   Lowest  Highest 

mg.  mg.                                                      mg.  mg. 

per  L.  per  L.                                                     per  L.  per  L. 

Schwabish-Gmund  .  . .    27.6  116.0  Dresden    (winter)   ...      6.2  24.6 

Giesscn 19.7  42.4  Dresden    (summer)   .  .      2.6  6.5 

Halle 14.9  72.5  Copenhagen 13.0         

Christina 11.0  Leipsic 3.8  11.5 

Hamburg 10.9  43.3  Wurzburg 3.0  8.1 

Berlin 10.3  50.0  Helingfors 1.8         

Munich 9.0  27.9 


370  BULLETIN  No.  236  [December, 

Some  of  the  foregoing  data  represent  unusual  and  extreme  con- 
ditions and  were  originally  published  with  the  object  of  shocking 
the  public  into  demanding  greater  cleanliness.  In  presenting  the  data, 
Grosse-Bohle  points  out  that  they  indicate  a  much  wider  range  of 
cleanliness  in  milk  supplies  than  actually  exists.  One  common  and 
important  source  of  variation  in  these  reports  arises  from  the  dif- 
ferent methods  followed  in  reporting  observed  results.  About  80  per- 
cent of  fresh  cow  dung  is  water.  Some  observers,  thinking  that  the 
dirt  in  milk  came  from  fresh  cow  dung,  and  feeling  that  the  small 
amount  of  dirt  recovered  by  them  did  not  fairly  represent  the  dirt 
entering  the  milk,  multiplied  their  actual  findings  by  five  and  re- 
ported the  resulting  figure  as  the  dirt  in  milk.  Some  multiplied  their 
findings  by  ten  and  others  used  different  factors.  As  has  already 
been  pointed  out,  moist  cow  dung  practically  never  enters  milk. 

In  the  case  of  the  figures  given  in  the  above  table,  it  is  impossible 
in  most  cases  to  learn  the  detailed  methods  of  sampling.  It  has  been 
the  practice  in  some  cases  to  prepare  samples  by  taking  the  last  of 
a  large  can  of  milk,  knowing  that  such  samples  would  include  prac- 
tically all  of  the  sediment  from  the  entire  can.  Results  from  such 
samples  are  often  forty  or  more  times  higher  than  would  be  shown 
by  a  truly  representative  sample.  These  figures  are  subject  to  con-- 
siderable  variation  depending  upon  whether  the  samples  were  taken 
immediately  after  the  milking,  when  the  amount  of  dirt  is  at  its  maxi- 
mUm,  or  at  some  other  stage  on  the  way  to  the  consumer. 

The  above  measurements  all  refer  to  European  conditions  and  there 
is  an  almost  entire  lack  of  information  regarding  the  dirt  content  of 
American  milk  supplies.  At  Chicago,  filtration  test  records  of  the 
dirt  content  of  milk  have  been  kept  since  1910.  The  amount  of  dirt 
in  the  milk  is  estimated  by  comparing  the  cotton  disk,  thru  which 
one  pint  of  milk  has  passed,  with  similar  disks  thru  which  suspensions 
of  known  amounts  of  dirt  have  been  filtered.  Of  111  samples  collected 
on  November  15,  1910,  from  the  40-quart  cans  of  the  farmers,  9  per- 
cent contained  not  more  than  one-half  milligram  of  dirt  per  pint  and 
were  graded  as  "good;"  26  percent  contained  one  to  two  milligrams 
and  were  graded  as  "fair;"  and  65  percent  contained  three  to  nine 
milligrams  and  were  graded  as  "bad."17  While  the  number  of  sam- 
ples is  too  small  to  be  taken  as  a  measure  of  Chicago  conditions  at  that 
date,  it  was  evidently  presented  as  fairly  typical  of  those  conditions. 


1921}          GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIRT  371 

EXPERIMENTAL  RESULTS 
PLAN  OF  THE  EXPERIMENTS 

The  absence  of  satisfactory  information  as  to  the  amount  of  dirt 
finding  its  way  into  milk  under  American  dairy  conditions,  and  as 
to  the  effect  of  this  dirt  upon  the  germ  count  of  milk,  suggested  that 
further  information  regarding  these  points  was  desirable. 

The  observations  here  reported  are  divided  into  three  general 
groups : 

First,  there  are  observations  upon  the  germ  count  of  the  milk 
from  cows  in  three  different  barns.  The  cows  in  each  barn  differed  in 
their  cleanliness,  but  all  of  them  were  kept  reasonably  clean.  These 
observations  extended  over  about  two  years  and  include  1,665  samples 
of  milk. 

Second,  there  is  given  the  results  of  a  brief  but  intensive  study  of 
the  bacterial  count  and  the  dirt  content  of  the  milk  from  the  cows 
in  one  of  the  barns  previously  studied,  after  the  cows  had  been  allowed 
to  become  excessively  dirty.  This  study  includes  the  results  from 
about  250  samples  of  milk. 

Third,  the  large  amount  of  germ  life  added  to  the  milk  by  a  rela- 
tively small  amount  of  dirt  from  the  excessively  dirty  cows  seemed 
to  call  for  an  explanation.  This  was  sought  in  a'  further  study  of 
the  dirt  from!  the  coats  of  the  cows. 

Technic. — The  technic  employed  in  the  first  group  of  observations 
has  already  been  given  in  detail  in  Bulletin  199  ]8  of  this  Station,  and 
that  employed  in  the  two  other  groups  was  essentially  the  same.  The 
bacterial  count  was  made  from  lactose  agar  plates,  incubated  suc- 
cessively for  5  days  at  20°C.,  and  2  days  at  37°C.  Where  special 
technic  was  made  necessary  by  the  nature  of  the  experiment,  it  is 
described  in  connection  with  the  experiment. 

EFFECT  OF  DIRT  FROM  RELATIVELY  CLEAN  Cows 

The  detailed  results  of  a  study  of  the  germ  count  in  the  milk  of 
138  cows,  housed  in  three  different  barns,  is  given  in  Bulletin  199. 
In  this  study  the  small-topped  milk  pails  were  carefully  steamed  and 
protected  from  contamination  up  to  the  moment  when  the  milking 
began.  The  samples  for  germ  count  were  taken  from  the  milk  of 
individual  cows  when  the  milker  brought  it  in  pails  from  the  barn 
into  the  adjacent  milk  room.  The  germ  count  found  in  these  samples 
included  the  germs  from  two  sources:  first,  the  udder;  and  second, 
those  brought  in  by  the  dirt  falling  into  the  milk. 

The  average  germ  count  obtained  from  the  milk  from  each  of  the 
three  barns  was  very  low,  being  2,639  per  cc.  for  Barn  I ;  920  per  cc. 
for  Barn  II ;  and  5,777  per  cc.  for  Barn  III. 


372  BULLETIN  No.  236  [December, 

It  has  been  shown  19  that  ordinarily  the  germ  count  of  the  milk 
as  it  comes  from  the  udder  is  about  500  per  cc.  Occasionally  the  count 
is  much  higher.  In  the  case  of  Barn  I  the  udder  of  a  single  cow  con- 
tributed germs  so  freely  that  had  her  samples  been  omitted  the  average 
germ  count  of  the  milk  in  that  barn  (2,639  per  cc.)  would  have  been 
reduced  to  approximately  1,000  per  cc.  Additional  study  showed 
that,  altho  apparently  healthy,  this  particular  cow  persistently  gave 
milk  with  a  high  germ  content,  the  source  of  which  was  her  udder. 
Considering  the  remaining  cows  in  Barn  I,  and  allowing  500  per  cc. 
for  the  germ  life  from  the  normal  udder,  there  remains  a  germ  count 
of  approximately  500  per  cc.  due  to  the  dirt  entering  the  milk. 

Barn  I,  which  contained  about  40  pure-bred  cows,  was  being  daily 
inspected  by  visitors,  and  the  cows  were  frequently  in  the  judging 
ring  for  class  or  exhibition  purposes.  The  cows  were  carefully  bedded 
and  groomed,  the  interior  of  the  barn  was  kept  freshly  painted,  the 
floors  were  scrubbed  and  flushed  with  water,  and  the  cows  were  kept 
unusually  clean.  While  the  attention  to  the  cleanliness  of  the  cows 
was  not  so  extreme  as  in  many  barns  where  certified  milk  is  produced, 
the  general  appearance  of  the  barn  and  the  cleanliness  of  the  cows 
were  roughly  comparable  with  the  conditions  often  surrounding  the 
production  of  certified  milk. 

In  Barn  II,  udder  conditions  appeared  to  be  entirely  normal.  Mak- 
ing the  same  allowance  of  500  per  cc.  for  germs  from  the  udder,  there 
remains  of  the  original  germ  count  of  920  per  cc.  a  germ  count  of 
approximately  500  per  cc.  to  be  accounted  for  on  the  basis  of  dirt. 

Barn  II  contained  about  40  grade  cows  which  were  used  in  various 
experiments.-  The  brick  side-walls  were  unfinished  and  the  planks 
of  the  joists  and  the  floor  above  were  rough  and  unpainted.  The 
length  of  the  stanchion  was  adjusted  to  the  need  of  the  individual 
cow,  and  bedding  was  ample  without  being  abundant.  Traces  of  dirt 
and  dried  manure  were  usually  to  be  found  on  the  flanks  of  a  number 
of  the  cows,  but  the  amount  of  this  material  was  always  small.  The 
conditions  of  cleanliness  in  Barn  II  were  fairly  comparable  with  those 
of  the  better  class  of  dairies  producing  milk  for  city  supply.  This 
barn  was  farther  away  and  visitors  were  not  so  common  as  at  Barn  I, 
but  the  lack  of  cleanliness  in  Barn  II  was  sufficiently  evident  to  occas- 
ionally excite  unfavorable  comment. 

Conditions  in  Barn  III  differed  from  those  in  either  of  the  other 
barns.  As  shown  by  a  later  study,  the  results  of  which  are  given  on 
page  376,  the  germ  count  from  the  udder  of  a  number  of  these  cows 
was  higher  than  the  normal,  and  the  average  germ  count  coming  from 
the  udder  was  probably  about  1,000  per  cc.  Figuring  from  the  orig- 
inal germ  count  of  5,777  per  cc.,  this  leaves  a  germ  count  of  about 
4,500  per  cc.  to  be  accounted  for  on  the  basis  of  the  dirt. 


1921]          GERM  CONTENT  OP  MILK  AS  INFLUENCED  BY  VISIBLE  DIRT  373 

Barn  III  contained  about  10  grade  cows.  It  had  a  dirt  floor,  with 
no  provision  for  drainage.  In  this  barn  the  cows  were  allowed  to 
run  loose.  Straw  was  added  to  absorb  the  liquid  and  cover  the 
manure,  and  the  resulting  accumulation  became  two  to  four  feet  deep 
before  it  was  removed  twice  a  year.  Clean  straw  was  supplied  abun- 
dantly, and  in  the  main  the  coats  of  the  cows  remained  fairly  clean, 
tho  the  condition  of  the  stable  floor  and,  to  some  extent,  the  coats  of 
the  cows  would  undoubtedly  have  called  forth  a  protest  from  a  city 
dairy  inspector.  While  the  general  conditions  of  cleanliness  in  Barn 
III  were  little  better  than  those  of  average  dairies  of  a  generation  ago, 
the  liberal  use  of  bedding  resulted  in  a  cleanliness  of  the  coats  of 
the  cows  which  was  roughly  comparable  with  that  in  many  market 
milk  dairies. 

Having  in  mind  the  increase  in  germ  count  resulting  from  the 
dirt  entering  the  milk  and  the  general  conditions  of  cleanliness  in  the 
barns,  attention  may  be  directed  toward  the  significance  of  the  ob- 
served facts.  The  observations  in  connection  with  Barn  I  suggest  that 
the  dirt  entering  the  milk  under  anything  less  than  good  certified- 
milk  conditions  results  in  an  increase  of  about  500"  per  cc.  in  the 
germ  count.  The  observations  in  connection  with  Barn  II  show  that 
when  the  conditions  of  cleanliness  are  no  better  than  those  found  in 
the  better  class  of  ordinary  farm  dairies,  the  dirt  entering  the  milk 
produces  approximately  the  same  increase  in  germ  count  as  noted  in 
Barn  I. 

The  explanation  for  these  identical  results  under  apparently 
widely  differing  conditions  lies  in  the  source  of  the  dirt.  Under  the 
conditions  obtaining  in  these  two  barns,  the  material  falling  into  the 
milk  was  practically  the  same,  consisting  of  hair  and  dandruff  from 
the  udder  and,  to  a  slight  extent,  from  the  flank.  While  the  amount 
of  falling  hair  varies  with  the  time  of  year,  the  amount  of  dandruff 
remains  practically  constant. 

In  Barn  III  a  distinctly  different  situation  was  evident.  Here 
the  conditions  of  cleanliness  were  roughly  comparable  with  those  of 
ordinary  dairies  during  the  winter  season,  and  the  increase  in  germ 
count  due  to  dirt  was  about  4,500  per  cc.  In  this  barn  the  hair  and 
dandruff  falling  into  the  milk  were  supplemented  by  various  other 
forms  of  dirt. 

EFFECT  OF  DIRT  FROM  EXTREMELY  DIRTY  Cows 

The  barn  conditions  already  described  are  representative  of  dairy 
conditions  ranging  from  very  good  to  rather  questionable.  In  order 
to  cover  the  subject  it  was  desirable  to  study  the  milk  produced  by 
extremely  dirty  cows.  It  is  the  unwritten  law  of  public  institutions 
that  dairy  cows  must  be  kept  clean,  and  accordingly  it  was  difficult 
to  provide  suitable  material  for  such  study.  In  the  work  already 


374  BULLETIN  No.  236  [December, 

described,  the  cows  were  allowed  to  become  so  dirty  as  to  provoke 
unfavorable  comment. 

In  the  winter  of  1916,  taking  advantage  of  a  quarantine  due  to  a 
neighboring  outbreak  of  foot-and-mouth  disease,  the  cows  in  Barn 
III  were  allowed  to  become  extremely  dirty.  The  accumulation  of 
manure  on  the  floor  of  the  stable  in  which  the  cows  were  loose  became 
about  four  feet  deep.  Practically  no  attempt  was  made  to  clean  the 
cows  for  some  months.  Dried  feces  accumulated  on  the  flanks  and 
abdomens  of  the  cows,  and  these  animals  were  fairly  representative 
of  extremely  dirty  dairy  conditions.  The  condition  of  the  coat  of 
one  of  these  cows  at  the  time  of  this  study  is  shown  on  page  391. 

Plan  of  the  Study 

When  the  cows  and  their  surroundings  had  become  representative 
of  extremely  dirty  dairy  conditions,  the  study  of  the  milk  was  begun. 
This  study  included  a  determination  of  the  germ  count  and  of  the 
diet  content  of  the  milk  of  seven  cows.  These  determinations  were 
made  in  three  series  of  ten  milkings  each,  and  in  addition  the  germ 
count  of  the  milk  directly  from  the  udder  of  each  cow  was  determined 
at  six  separate  milkings.  Accordingly,  germ  counts  were  made  upon 
252  milk  samples. 

The  three  series  differed  from  each  other  in  that  in  the  first  series 
the  milk  pail  was  the  small-topped  one,  with  an  oval  opening  5x7 
inches,  used  in  the  previously  described  studies  in  Barns  I,  II,  and 
III;  in  the  second  series  an  ordinary  open-topped  milk  pail,  having 
a  diameter  of  about  twelve  inches,  was  used;  and  in  the  third  series 
conditions  were  the  same  as  in  the  first,  except  that  the  coats  of  the 
cows  had  been  thoroly  cleaned.  The  milk  pails  in  all  cases  were  care- 
fully steamed  and  protected  until  used. 

The  sample  for  determining  the  germ  count  was  taken  from  the 
milk  of  each  cow  as  the  milk  came  in  the  pail  from  the  stable  to  the 
milk  room.  The  dirt  determinations  were  made  from  the  unstrained 
milk,  collected  in  eight-gallon  cans.  The  amount  of  this  milk  at  each 
milking  varied  between  112  and  168  pounds. 

Determining  the  Dirt  in  the  Milk 

A  combination  of  sedimentation  and  centrifugal  force  was  used  in 
determining  the  amount  of  dirt.  After  the  cans  of  milk  had  stood 
for  eight  hours,  the  bulk  of  the  milk  was  siphoned  (the  first  five 
samples  were  poured)  thru  a  weighed  100-mesh  sieve.  The  remaining 
milk  was  poured  thru  the  same  sieve  but  was  collected  in  a  glass 
cylinder.  The  cans  were  then  rinsed  and  the  rinsings  poured  thru 
the  sieve  into  the  cylinder.  The  sieve  was  washed  with  water  and  a 
little  alcohol  to  free  it  from  milk  and  fat,  and  these  washings  were 
added  to  the  cylinder.  The  sieve  was  then  dried  and  weighed.  The 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIET 


375 


material  retained  by  the  sieve  was  largely  hair,  bits  of  straw,  and 
what  appeared  to  be  scales  from  the  skin  of  the  cow. 

Bichlorid  of  mercury  was  added  to  the  material  in  the  cylinder 
as  a  preservative,  and  after  the  cylinder  stood  eight  hours  the  upper 
portion  of  the  fluid  was  siphoned  off.  The  remaining  material  was 
centrifuged  for  half  an  hour,  the  liquid  poured  off,  the  sediment 
again  suspended  in  distilled  water,  and  the  centrifuging  repeated. 
The  liquid  was  then  poured  off  and  the  sediment,  washed  into  a 
weighed,  folded  filter,  was  dried  and  weighed. 

Milligrams  per  liter  is  probably  the  best  form  for  expressing  the 
dirt  content  of  milk,  because  the  liter  is  the  most  widely  recognized 
unit  of  volume.  However,  the  volume  of  the  U.  S.  quart  is  almost 
the  same  as  that  of  the  liter,  and  the  quart  is  the  accepted  standard 
for  retailing  milk  in  this  country.  Since  it  is  doubtful  if  the  difference 
in  the  dirt  content  of  a  quart  and  of  a  liter  can  be  detected  by  the 
available  methods  of  measuring  the  dirt  in  milk,  it  will  serve  the 
present  purposes  better  to  express  the  dirt  measurements  in  milligrams 
per  quart.  In  round  numbers  one  milligram  of  dirt  per  quart  is  one 
part  of  dirt  to  one  million  parts  of  milk. 

Series  1 — When  tJie  Small-Topped  Pail  Was  Used 

In  the  previous  studies  in  Barns  I,  II,  and  III,  the  small-topped 
milk  pail  was  used.  In  order  to  obtain  comparable  data,  it  was  again 
used  in  the  first  series  of  samples.  The  germ  count  obtained  from 
the  samples  of  milk  drawn  from  each  of  seven  extremely  dirty  cows 
into  small-topped  pails  at  ten  successive  milkings  is  given  in  Table  1. 

TABLE  1. — GERM  COUNT  OF  MILK  DRAWN  FROM  DIRTY  Cows  IN.TO 
SMALL-TOPPED  PAIL 


No.  of  cow  .... 

1019 

1032 

1033 

1034 

1036 

1037 

1038 

Feb.  24  a.m.  .  . 

per  cc. 
12775 

per  cc. 
61  900 

per  cc. 
9925 

per  cc. 
10425 

per  cc. 
13850 

per  cc. 
2  600 

per  cc. 
7350 

24  p.m.  .  . 
25  a.m.  .  . 

17375 
5355 

21  725 
18900 

5  125 
10650 

15525 
14300 

3800 
11  850 

3650 
7740 

4000 
20275 

25  p.m.  .  . 
26  a.m.  .  . 

44325 
4600 

4200 
11  375 

10650 
13  125 

10700 
70500 

8  125 
10  125 

8  725 
7  100 

4425 
7950 

28  a.m.  .  . 

2850 

7325 

9925 

5725 

3  000 

3  625 

5450 

28  p.m.  .  . 
29  a.m.  .  . 

11  800 
9267 

14875 
31  375 

11  125 
3  125 

7975 
13675 

1  885 
5300 

1  085 
3  275 

1  295 
1  800 

29  p.m.  .  . 
Mar.  1  a.m.  .  . 

90000 
39200 

10700 
6425 

6900 
62900 

10050 
8  133 

3650 
3050 

3250 
2650 

3  700 
5425 

Average  

23  755 

18880 

14345 

16701 

6463 

4370 

6  167 

General  average 12  954 


376 


BULLETIN  No.  236 


[December, 


The  germ  count  given  in  this  table  is  the  combined  result  of  the 
germ  life  derived  from  the  udder  and  the  germ  life  carried  into  the 
milk  by  the  dirt.  To  find  the  part  of  this  due  to  dirt  it  is  necessary 
to  find  the  germ  count  of  the  milk  coming  from  the  udder.  Samples 
of  milk  for  this  measurement  were  carefully  drawn  from  the  udder 
directly  into  sterile  tubes  when  the  cows  were  about  half  milked,  and 
such  samples  were  taken  from  each  of  the  seven  cows  at  six  successive 
milkings.  The  results  of  the  germ-count  determinations  of  such 
samples  are  given  in  Table  2. 

TABLE  2. — GERM  COUNT  OF  MILK  DIRECT  PROM  THE  UDDER 


No.  of  cow  .... 

1019 

1032 

1033 

1034 

1036 

1037 

1038 

Mar.  20  p.m...  . 
21  a.m.... 
21  p.m.... 
22  a.m..  .  . 
23  a.m..  .  . 

per  cc. 

V675 
1  390 
1  095 

per  cc. 
345 
575 
735 
905 
620 

per  cc. 
2  130 
525 
2280 
4230 
905 

per  cc. 
855 
1  755 
430 
1  065 

per  cc. 
750 
475 
540 
640 
555 

per  cc. 
1995 
435 
370 
360 
1  150 

per  cc. 
150 
190 
50 
345 
820 

23  p.m.... 

1  415 

290 

1  140 

530 

2480 

1  080 

420 

Average  

1  244 

578 

1868 

927 

907 

898 

329 

General  average 964 


These  determinations  of  the  germ  count  of  the  milk  as  it  came 
from  the  udder  show  that  while  there  was  considerable  fluctuation 
in  the  successive  samples  from  the  same  cow  and  distinct  differences 
in  the  germ  count  of  the  milk  from  different  cows,  the  average  addi- 
tion to  the  germ  count  due  to  udder  conditions  was  approximately 
1,000  per  cc. 

Since  the  results  given  in  Table  1  show  an  average  germ  count 
in  the  milk  of  12,954  per  cc.,  and  the  samples  from  the  udder  show 
an  average  count  of  964  per  cc.,  there  remain  approximately  12,000 
per  cc.  to  be  accounted  for  on  the  basis  of  the  dirt  falling  into  the 
milk  when  drawn  from  extremely  dirty  cows  into  small-topped  pails. 

The  amount  of  dirt  actually  recovered  from  the  milk  as  drawn 
from  the  dirty  cows  into  small-topped  pails  is  given  in  Table  3.  (It 
is  regrettable  that  the  data  in  Table  3  include  the  milk  from  only 
seven  of  the  ten  milkings  at  which  the  germ  count  was  determined. 
The  practical  difficulties  connected  with  finding  the  dirt  content  did 
not  permit  of  more  determinations.) 

The  material  retained  by  the  sieve  consisted  mainly  of  bits  of  hay 
and  straw,  hair,  and  dandruff.  It  chanced  that  this  and,  more  par- 
ticularly, the  later  tests  were  made  at  the  time  when  the  cows  were 
shedding  their  hair  freely.  The  greater  part  of  the  material  retained 
by  the  sieve  would  ordinarily  be  removed  by  the  straining  at  the 


1921] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIET 


377 


TABLE  3. — DIRT  AND  GERMS  IN  MILK  DRAWN  FROM  DIRTY  Cows  INTO  SMALL- 
TOPPED  PAIL 


Date 

Milk 

DIRT 

Bacteria 

On  sieve 

On  filter 

Total 

Per  quart 

Feb.    24  a.m  

Ibs. 
162.1 
148.1 
167.7 
148.9 
161.1 
142.1 
158.7 

mgs. 
236.6 
727.2 
518.4 
352.4 
512.7 
370.0 
435.6 

mgs. 
250.7 
259.6 
66.2 
96.2 
83.8 
133.9 
82.5 

mgs. 
487.3 
986.8 
584.6 
448.6 
596.5 
503.9 
518.1 

mgs. 
6.467 
14.325 
7.495 
6.466 
7.961 
7.624 
7.019 

per  cc. 
12734 
8416 
12400 
12  115 
17896 
14800 
19577 

24  p.m  

25  a.m  

25  p.m  

26  a.m  

29  p.m  

Mar.     1  a.m  

Average         

8.1 
7.1 

14000 

Average  omitting  2d  sample  

farm,  and  if  missed  there,  would  be  removed  by  the  strainers  at  the 
milk  plant.  In  all  except  the  first  test  in  the  Table  3,  the  dirt  re- 
tained by  the  sieve  amounted  to  more  than  50  percent  of  the  total 
dirt  recovered  from  the  milk,  and  the  average  for  the  seven  tests 
was  76  percent. 

The  dirt  retained  by  the  filter  would  probably  have  passed  thru 
ordinary  strainers  and  would  hardly  have  been  removed  by  anything 
employed  in  the  milk  business,  except  centrifugal  force,  such  as  that 
exerted  by  the  milk  clarifier.  Accordingly,  it  represents  the  dirt 
which  remains  in  the  milk  as  delivered  to  the  consumer*  except  in 
those  cases  where  a  clarifier  is  employed. 

It  will  be  noted  that  the  proportion  of  dirt  present  in  the  milk 
on  different  days  was  fairly  constant,  being  between  6.5  and  7.9  milli- 
grams per  quart,  except  for  the  second  milking,  when  it  was  14.3 
milligrams  per  quart.  It  will  be  noted  that  at  this  milking  the  ex- 
cessive amount  of  dirt  was  retained  by  the  sieve.  As  a  matter  of 
fact,  this  excessive  weight  of  dirt  was  largely  due  to  a  piece  of  hay 
which  was  floating  in  the  milk.  The  dirt  content  of  the  entire  506.4 
quarts  of  milk  averaged  8.1  milligrams  per  quart,  or  if  the  second 
milking  be  omitted,  the  average  was  7.1  milligrams  per  quart. 

Not  the  least  surprising  of  the  data  are  those  given  in  the  column 
showing  the  bacteria  per  cubic  centimeter.  The  germ  count  of  the 
milk  for  each  day  was  calculated  as  the  total  germ  count  of  the  milk 
of  all  the  cows,  divided  by  the  total  number  of  cubic  centimeters  of 
milk.  It  will  be  noted  that  the  lowest  germ  count  was  found  on  the 
day  when  the  proportion  of  dirt  in  the  milk  was  highest,  but  it  has 
already  been  explained  that  in  this  case  the  excess  dirt  consisted  of 
a  bit  of  hay  which  undoubtedly  carried  but  little  germ  life. 

Taken  as  a  whole  these  results  indicate  a  surprisingly  small  varia- 
tion in  germ  content  in  this  milk,  coming  as  it  did  from  extremely 


378  BULLETIN  No.  236  [December, 

dirty  cows  and  carrying  a  relatively  large  amount  of  dirt.  To  many 
the  low  germ  count  of  the  milk  obtained  under  these  circumstances 
will  be  even  more  surprising.  Had  all  this  milk  been  produced  at 
one  time  and  the  milk  carefully  mixed,  a  representative  sample  should 
have  given  a  germ  count  of  14,000  per  cc.  In  this  connection  it  should 
be  remembered  that  this  germ  count  was  made  after  an  incubation 
of  the  plates  for  five  days  at  20° C.  anql  two  days  at  37°C.,  instead 
of  the  single  incubation  for  two  days  at  37.5°  C.  required  by  the 
official  methods  of  routine  milk  examination.20 

This  longer  incubation  period  has  been  used  consistently  in  all 
of  these  research  studies  because  of  the  fact  that  it  gives  distinctly 
higher  germ  counts.  Had  these  samples  of  milk  been  given  the  official 
routine  bacteriological  examination,  the  majority  of  them  would  have 
been  reported  as  being  below  10,000  per  cc.,  which  is  set  as  the  upper 
limit  for  certified  milk. 

In  justice  to  certified  milk  it  should  be  made  clear  that  the  pro- 
duction of  certified  milk  is  surrounded  by  other  safeguards  in  addi- 
tion to  a  limit  of  10,000  per  cc.  germ  count,  but  the  illustration  is 
used  at  this  point  because  in  the  estimation  of  the  general  public  and 
too  often  in  the  thinking  of  health  officials,  a  count  of  10,000  per  cc. 
is  taken  as  complete  evidence  that  the  milk  in  question  has  been  pro- 
duced under  the  most  exacting  conditions  of  cleanliness.  The  data 
given  in  Table  3  make  it  clear  that  a  germ  count  of  10,000  per  cc. 
does  not  necessarily  mean  anything  of  the  sort. 

Series  II — When  the  Ordinary  Milk  Pail  Was  Used 

In  commercial  dairies,  under  the  exceptional  conditions  where  the 
cows  would  be  permitted  to  become  as  dirty  as  those  in  this  study, 
the  ordinary  type  of  open  milk  pail  would  often  be  used.  Under 
these  conditions  the  maximum  amount  of  dirt  would  fall  into  the  milk. 
In  order  to  measure  the  dirt  under  the  worst  conditions,  the  seven 
cows  were  milked  into  open-topped  pails  for  ten  successive  milkings. 
A  sample  of  the  milk  from  each  cow  was  taken  and  its  germ  count 
determined.  The  results  of  these  determinations  are  given  in  Table  4. 

The  data  in  Table  4  show  that  the  germ  count  of  the  samples  from 
the  various  cows  averaged  between  28,485  and  10,783  per  cc.  They 
also  show  that  there  were  fairly  characteristic  differences  in  the  germ 
counts  from  the  different  cows,  the  samples  from  Cow  1019  being 
quite  consistently  high  in  germ  count,  while  those  from  Cows  1037 
and  1038  are  quite  consistently  low.  Reference  to  Table  1  will  show 
that  practically  the  same  relations  obtained  during  the  first  series  of 
samples.  The  explanation  does  not  seem  to  lie  in  the  degree  of  dirti- 
ness of  the  cows,  since  Cow  1019  is  at  times  recorded  as  "moderately 
dirty,"  while  Cows  1037  and  1038  are  at  times  among  those  marked 
"extremely  dirty."  The  explanation  of  the  high  count  from  Cow 


1921} 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIRT 


379 


TABLE  4. — GERM  COUNT  OF  MILK  DRAWN  FROM  DIRTY  Cows  INTO  OPEN- 
TOPPED  PAIL 


No.  of  cow  .... 

1019 

1032 

1033 

1034 

1036 

1037 

1038 

Mar.  1  p.m. 
2  a.m. 

per  cc. 
19  125 
21  150 

per  cc. 
45  100 
13000 

per  cc. 
64250 
3865 

per  cc. 
7425 
10657 

per  cc. 
6875 
5750 

per  cc. 
'  4650 
7450 

per  cc. 
9425 
10400 

2  p.m. 
3  a.m. 

68925 
13800 

25975 
27400 

11  300 
1  550 

17833 
18450 

6  100 
58800 

9000 
3400 

7350 

4825 

3  p.m. 
6  a.m. 

45550 
6300 

10600 
22550 

2750 
11  125 

9075 
9625 

18500 
4300 

4633 
9025 

44750 
8150 

6  p.m. 
7  p.m. 
8  a.m. 

10050 
21  200 
20  100 

4  100 
45375 
15  100 

5375 
3  125 
7  150 

20350 
15350 
6  150 

4075 
94000 
9750 

5500 
36  175 
5700 

9000 
27  175 
19800 

8  p.m. 

58650 

39825 

5450 

16750 

34  150 

22300 

3525 

Average  

28485 

24902 

11  594 

13  167 

24230 

10783 

14  440 

General  average 18  229 


1019  probably  lies  in  the  fact  that  it  was  so  difficult  to  milk  her  that 
twice  the  ordinary  time  was  consumed  in  the  milking  process.  The 
prolonged  agitation  of  the  udder  above  the  pail  allowed  more  dirt 
to,  fall  into  the  milk. 

When  one  remembers  that  these  samples  came  from  milk  drawn 
from  extremely  dirty  cows  into  open-topped  pails,  the  most  surpris- 
ing feature  of  the  data  is  the  low  bacterial  count.  Forty-six  percent 
of  the  samples  gave  a  germ  count  under  10,000  per  cc.  The  general 
average  of  all  of  the  samples  was  only  18,229  per  cc.,  and  there  is  but 
one  sample  among  the  seventy  with  a  germ  count  above  60,000  per 
cc.,  which  marks  the  upper  limit  for  New  York  Grade  A  milk.  It 
should  further  be  remembered  that  the  method  of  incubation  used 
with  these  counts  should  lead  to  counts  at  least  20  percent  higher 
than  would  be  secured  by  the  official  methods  used  in  routine  milk 
control. 

In  considering  the  relation  of  these  germ  counts  to  dirt  as  a  source 
of  the  germs,  it  should  be  remembered  that  allowance  for  the  udder 
content  should  be  made  according  to  the  results  shown  in  Table  2. 

The  amount  of  dirt  actually  recovered  from  the  milk  as  drawn 
from  the  dirty  cows  into  open-topped  pails  is  given  in  Table  5. 

In  considering  the  data  given  in  Table  5,  it  is  at  once  apparent 
that  the  dirt  determinations  from  the  last  three  samples  are  abnormal. 
The  results  are  here  given  just  as  determined,  tho  the  reason  for 
the  abnormality  was  understood  at  the  time  of  determination.  On 
these  three  days  the  milk  promptly  became  ropy  and  it  was  not  pos- 
sible to  separate  all  of  the  milk  from  the  sediment.  The  difficulty  is 
most  evident  in  material  retained  by  the  sieve,  tho  the  results  from 
the  filter  were  also  affected.  If  these  abnormal  results  were  included, 


380 


BULLETIN  No.  236 


[December, 


TABLE  5. — DIRT  AND  GERMS  IN  MILK  DRAWN  FROM  DIRTY  Cows  INTO  OPEN- 
TOPPED  PAIL 


Date 

Milk 

.  .                 DIRT 

Bacteria 

On  sieve 

On  filter 

Total 

Per  quart 

Mar    1  p.m  

Ibs. 
140.0 
162.1 
143.8 
158.0 
140.5 
149.2 
132.8 
150.7 

mgs. 
574.1 
871.7 
695.6 
562.7 
589.9 
1  103.5 
1  029.9 
1  309.2 

mgs. 
107.7 
108.1 
66.9 
98.4 
75.5 
119.5 
271.4 
157.7 

mgs. 
681.8 
979.8 
762.5 
661.1 
665.4 
1  223.0 
1  301.3 
1  466.9 

mgs. 
10.5 
13.0 
11.4 
9.0 
10.2 
17.6 
21.1 
16.6 

per  cc. 
22  179 
9  164 
17470 
15959 
17929 
8250 
35623 
22303 

2  a.m  

2  p.m  

3  a.m  

3  p.m  

6  p.m  

7  p.m  

8  p.m  

Average  

14.2 
10.8 

18244 

Average  omitting  last  3  samples  

14.2  milligrams  of  sediment  per  quart  would  be  shown,  or  if  the 
calculations  were  restricted  to  the  five  days  when  conditions  were 
normal,  the  average  dirt  content  would  be  10.8  milligrams  per  quart. 
Of  this  amount  88  percent  was  retained  by  the  sieve. 

The  calculation  of  the  bacterial  count  for  each  milking  shows  that 
at  two  milkings  the  entire  product  of  the  seven  cows  had  a  germ 
count  of  less  than  10,000  per  cc.,  and  that  at  no  milking  did  it  go 
above  36,000  per  cc.  The  average  germ  count  for  the  entire  1,177 
pounds  of  milk  was  18,244  per  cc. 

.Jutr/oo  • 
Series  III — When  the  Cows  Had  Been  Cleaned 

In  Series  I  and  II  are  given  the  germ  counts  found  and  the  dirt 
recovered  from  the  milk  of  seven  extremely  dirty  cows  when  they 
were  milked  into  small-topped  and  into  ordinary  pails.  The  cows 
were  dirty  as  a  result  of  lying  upon  an  accumulation  of  straw  and 
their  own  manure,  which  at  the  time  of  the  study  was  about  four 
feet  deep. 

In  order  to  bring  out  more  clearly  the  effect  of  the  condition  of 
the  coat  of  the  cow  upon  the  cleanliness  and  germ  count  of  the  milk, 
the  coats  of  the  cows  were  cleaned,  but  all  of  the  other  factors  in  the 
situation  remained  unchanged.  For  ten  successive  milkings  these 
cleaned  cows  were  milked  into  small-topped  pails,  and  the  germ  count 
and  the  dirt  content  were  determined  as  in  the  preceding  series.  The 
results  are  recorded  in  Table  6. 

It  will  be  seen  from  this  table  that  the  cleanliness  of  the  coat  of 
the  cows  really  lasted  just  one  day.  Before  each  successive  milking, 
the  milker  made  some  effort  to  remove  the  dirt  evident  upon  the  cow, 
and  the  resulting  cleanliness  of  the  cows  was  in  marked  contrast  to 
their  former  condition,  but  sufficient  labor  was  not  available  to  keep 
the  coats  of  the  cows  clean  when  they  were  living  on  the  top  of  a 


1921] 


GEKM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIET 


381 


TABLE  6. — GERM  COUNT  OF  MILK  DRAWN  FROM  CLEANED  Cows  INTO 
SMALL-TOPPED  PAIL 


No.  of  cow.  .  .  . 

1019 

1032 

1033 

1034 

1036 

1037 

1038 

Mar.  17  a.m...  . 
18a.m.... 
"   18p.m.... 
"   20  a.m.. 

per  cc. 
3000 
55600 
14400 

per  cc. 
5900 
3  600 
4700 
4  600 

per  cc. 
4  150 
38850 
8575 
4  900 

per  cc. 
6550 
4500 
7650 
5  500 

per  cc. 
3250 
4900 
1  550 
2  250 

per  cc. 
1  975 
8333 
850 
2  750 

per  cc. 
1  150 
3000 
2650 
2  800 

20p.m.... 

25025 

6  338 

3  110 

5  163 

4  270 

1  385 

"   21  a.m...  . 
"   21p.m.... 
"   22a.m.... 
"   23a.m.... 
23p.m.... 

3  680 
5576 
7975 
22775 
3415 

4590 
6720 
6  170 
14305 

3278 

6510 
7355 
10000 
9785 
2210 

10725 
16700 
9300 
8050 
4375 

3525 
3510 
3795 
10880 
5040 

3200 
5  100 
2910 
3  100 
4420 

7710 
2205 
4080 
4  105 
1890 

Average  

15716 

6020 

9544 

7851 

4297 

3626 

3097 

General  average 7  165 


manure  heap.  While  the  attempt  at  keeping  the  cows  clean  was  not 
entirely  successful,  the  effect  of  their  increased  cleanliness  upon  the 
milk  was  very  evident.  Only  15  percent  of  the  samples  gave  a  germ 
count  of  over  10,000  per  cc.,  and  the  average  of  the  68  samples  was 
7,165  per  cc. 

The  amount  of  dirt  actually  recovered  from  the  milk  as  drawn 
from  the  cleaned  cows  into  small-topped  pails  is  given  in  Table  7. 

TABLE  7. — ] 


Date 

Milk 

I 

>IRT 

Bacteria 

On  sieve 

On   filter 

Total 

Per  quart 

Mar.  17  a.m  

Ibs. 
145.6 

mgs. 
160.6 

mgs. 
7.6 

mgs. 
168.2 

mgs. 
2.48 

per  cc. 
3490 

18a.m  

143  3 

208  7 

26  0 

234  7 

3.52 

17  219 

"        18p.m  

128  1 

210  8 

54  5 

265  3 

4  45 

5  379 

"       20  a.m  

126  4 

142  6 

60  1 

202  7 

3  44 

3  672 

"       20p.m  

112.4 

249.8 

56.8 

306.6 

5.86 

6473 

"       21  a.m  

148  7 

222  3 

48  9 

271.2 

3  92 

5  650 

"       21  p.m  

134  4 

415  1 

79  1 

494  2 

7  91 

6  382 

"       22  a.m.  .  .    . 

155  0 

103  3 

75  6 

178  9 

2  54 

6  086 

23  a.m  

146.7 

392.9 

26.1 

419.0 

6.15 

9  108 

Average  

4.6 

7  117 

It  is  seen  from  this  table  that  the  dirt  removed  from  the  milk  of  the 
cleaned  cows  averaged  4.6  milligrams  per  quart.  This  amount  is 
directly  comparable  with  the  8.1  milligrams  per  quart  removed  from 
the  milk  of  the  dirty  cows  milked  into  small -topped  pails.  Accord- 
ingly, the  cleaning  of  the  cows  reduced  the  recoverable  dirt  by  44 
percent. 


382  BULLETIN  No.  236  [December, 

It  also  should  be  noted  that  the  sieve  recovered  83  percent  of  the 
dirt,  while  but  0.8  of  a  milligram  per  quart  was  recovered  by  the  filter. 

The  reduction  in  germ  count  is  also  interesting.  The  milk  when 
drawn  from  dirty  cows  into  small-topped  pails  gave  a  germ  count  of 
14,000  per  cc.,  while  the  milk  from  the  cleaned  cows  drawn  into  simi- 
lar pails  gave  a  germ  count  of  7,117  per  cc.  Allowing  1,000  per  cc. 
as  the  germ  life  from  the  udder,  it  will  be  seen  that  the  cleaning  of 
the  cows  reduced  the  dirt  in  the  milk  44  percent  and  the  germ  count 
due  to  dirt  46  percent. 

So  far  as  indicated  by  the  germ  count,  the  milk  from  the  cleaned 
cows  left  little  to  be .  desired.  It  chanced  that  two  of  the  highest 
counts  of  the  series  occurred  in  the  samples  on  the  morning  of  March 
18,  when  the  average  germ  count  for  the  milking  was  17,219  per  cc. 
The  combined  average  for  the  counts  of  the  other  eight  milkings, 
as  shown  in  Table  7,  was  but  5,780  per  cc. 

Discussion  of  the  Results  from  the  Three  Series 

The  data  from  the  three  series  of  observations  on  the  milk  of  the 
seven  cows  emphasise  two  points:  first,  that  the  amount  of  dirt  re- 
covered from  the  milk  is  small ;  second,  that  the  increase  in  the  germ 
count  due  to  dirt  is  slight. 

The  small  amount  of  dirt  entering  the  milk  was  not  due  to  any 
lack  of  dirt  on  the  cows.  The  dirt  entering  the  milk  during  the  milk- 
ing process  comes  mainly  from  the  surface  of  the  udder  and  to  a  less 
extent  from  the  flank.  Under  filthy  surroundings,  while  the  flank 
often  becomes  dirty,  the  udder  ordinarily  remains  fairly  clean,  even 
in  the  case  of  cows  with  large  udders.  During  milking  the  pail  is  at 
one  side,  not  directly  under  the  udder,  and  a  considerable  portion 
of  the  dirt  loosened  by  the  milking  process  falls  outside  of  the  pail. 

In  the  case  of  the  extremely  dirty  cows  milked  into  an  ordinary 
pail  having  a  diameter  of  about  twelve  inches,  the  dirt  recovered  from 
the  milk  amounted  to  10.8  milligrams  per  quart.  When  the  same 
cows  were  milked  into  a  pail  having  an  opening  5x7  inches,  the  re- 
covered dirt  amounted  to  8.1  milligrams  per  quart ;  or  if  the  milking 
where  the  total  dirt  was  increased  by  hay  falling  into  the  milk  while 
it  was  being  carried  from  the  stable  be  omitted,  the  average  was  7.1 
milligrams  per  quart.  These  figures  show  that  on  one  basis  of  calcula- 
tion the  dirt  kept  out  of  the  milk  by  the  small-topped  pail  amounted 
to  25  percent,  and  on  the  other  basis  to  34  percent,  of  that  entering 
the  open  pail.  Stocking  found  in  his  studies  that  a  similar  small- 
topped  pail  reduced  the  amount  of  dirt  entering  the  milk  by  40 
percent. 

At  the  first  milking  in  the  third  series  (the  series  in  which  the 
cows  were  cleaned) ,  the  dirt  recovered  amounted  to  only  2.5  milligrams 


19S1]          GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIRT  383 

per  quart.  While  not  a  sufficient  basis  for  generalization,  this  prob- 
ably indicates  what  may  be  expected  under  very  clean  conditions. 
On  this  basis  the  range  in  results  between  clean  and  extremely  dirty 
conditions  is  the  range  between  2.5  and  10.8  milligrams  of  dirt  per 
quart.  The  cleanliness  of  the  cows  during  the  third  series  would 
compare  favorably  with  the  cleanliness  of  a  majority  of  dairy  cows 
during  the  later  portion  of  the  winter,  and  the  average  of  the  dirt 
recovered  from  this  series  of  milkings  amounted  to  4.6  milligrams 
per  quart.  From  this  it  would  seem  that  milk  could  not  be  considered 
abnormally  dirty  until  the  recoverable  dirt  in  the  unstrained  milk 
amounted  to  at  least  5  milligrams  per  quart. 

The  possibility  of  judging  of  the  conditions  of  production  by  the 
dirt  recoverable  from  the  milk  is  further  complicated  by  the  fact 
that  thoro  straining  removes  75  percent  or  more  of  the  recoverable 
dirt.  This  means  that  even  in  the  dirtiest  milk  the  recoverable  dirt 
may  be  reduced  by  thoro  straining  to  about  2  milligrams  per  quart. 
When,  in  addition  to  the  straining  process  the  milk  is  later  exposed 
to  the  action  of  the  milk  clarifier,  the  amount  of  dirt  in  the  milk  as 
delivered  to  the  consumer  is  reduced  toward,  if  not  to,  the  vanishing 
point. 

In  computing  the  increase  in  germ  count  due  to  dirt  in  the  milk 
of  these  seven  cows,  the  germ  count  due  to  the  udder  may  be  con- 
sidered as  1,000  per  cc.  The  results  from  the  examination  of  the 
milk  indicate  that  when  the  cleanliness  of  the  cows  is  roughly  com- 
parable with  that  of  winter  conditions  in  ordinary  dairies,  and  the 
recoverable  dirt  amounts  to  4.6  milligrams  per  quart,  the  germ  count 
due  to  dirt  amounts  to  about  6,000  per  cc.  Where  the  cows  are  more 
dirty  and  the  recoverable  dirt  amounts  to  7.1  milligrams  per  quart, 
this  dirt  adds  13,000  per  cc.,  while  under  extremely  dirty  conditions 
the  recoverable  dirt  may  amount  to  10.8  milligrams  per  quart  and 
the  increase  in  germ  count  due  to  dirt  be  raised  to  about  17,000  per 
cc.  This  increase  of  17,000  per  cc.,  which  may  enter  with  the  dirt 
under  extreme  conditions,  taken  by  itself  seems  like  a  significant 
amount  of  contamination.  However,  it  becomes  a  small  and  uncer- 
tain part  of  the  50,000  to  70,000  bacteria  per  cc.  commonly  found  in 
market  milk  in  which  multiplication  of  bacteria  has  not  yet  occurred. 

To  those  who  rely  upon  the  germ  count  of  market  milk  to  indicate 
the  conditions  of  cleanliness  under  which  milk  is  produced  and 
handled,  these  results  cannot  be  otherwise  than  discouraging.  The 
results  are  not  open  to  criticism  of  the  manner  of  determining  the 
germ  count,  because  the  methods  employed  are  recognized  as  pro- 
ductive of  germ  counts  distinctly  higher  than  those  resulting  from 
routine  official  methods. 


384 


BULLETIN  No.  236 


[December, 


Germ  Count  of  the  Dirt  from  Extremely  Dirty  Cows 
It  will  be  noted  that  thruout  the  discussion  of  the  results  from 
these  three  series  of  studies  of  dirty  cows,  the  calculations  have  been 
based  upon  the  determined  dirt.  It  is  recognized  that  the  method 
used  in  determining  the  dirt  was  imperfect  and  that  undoubtedly 
some  of  the  dirt  was  not  recovered.  Again,  there  is  no  question  but 
that  some  of  the  dirt  passed  into  solution  and  thereby  escaped  detec- 
tion. It  is  important  to  know  the  extent  to  which  the  dirt  thus  over- 
looked should  modify  the  conclusions  drawn  from  data  concerning 
the  part  of  the  dirt  which  was  determined. 

While  the  accuracy  of  the  determinations  of  the  dirt  content  of 
this  milk  may  be  questioned,  the  determinations  of  the  relatively 
small  increase  in  germ  count  which  accompanied  the  additions  of  the 
dirt  to  the  milk,  can  hardly  be  doubted.  Since  the  germ-count  de- 
terminations are  the  portions  regarding  which  there  can  be  little 
question,  they  may  be  used  as  a  means  of  testing  the  accuracy  of 
the  dirt  determinations. 

The  milk  in  each  of  the  three  series  of  tests  amounted  to  about 
1,000  pounds  and  included  a  known  amount  of  dirt.  The  germ  count 
of  this  milk  was  carefully  determined.  From  these  data  it  is  possible 
to  compute  the  germ  count  of  the  dirt  recovered  from  the  milk.  All 
that  is  necessary  for  this  determination  is  to  find  the  total  germ 
count  of  the  milk,  subtract  the  1,000  per  ce.  due  to  udder  flora,  and 
divide  the  resulting  number  by  the  grams  of  dirt.  The  data  for  this 
calculation  for  each  of  the  three  series  are  given  in  Table  8. 

TABLE  8. — GERM  COUNT  OF  DIRT  RECOVERED  FROM  MILK 


Series 

Volume 
of 
milk 

Dirt 

found 

Germs  in 
milk 

Germs  from 
udder 

Germs  from 
dirt 

Germs  from 
1  pram  of 
dirt 

I.. 

Of. 

478  537 

gms. 
4.1258 

millions 
6700 

millions 
479 

millions 
6  221 

millions 
1  508 

II  

372  162 

3.7506 

5339 

327 

5012 

1  342 

Ill  

545  765 

2.5408 

3884 

546 

3339 

1  314 

The  data  in  Table  8  place  the  germ  count  of  the  dirt  recovered 
from  the  milk  at  approximately  1.5  billion  germs  per  gram.  Those 
who  are  familiar  with  the  germ  count  of  such  substances  as  milk  and 
soil  will  at  once  recognize  that  this  is  a  high  figure.  In  fact  it  is  so 
high  as  to  offer  some  basis  for  the  suggestion  that  this  large  amount 
of  germ  life  may  have  entered  the  milk  in  connection  with  a  larger 
amount  of  dirt  than  was  later  recovered  from  the  milk. 

Manifestly  the  most  direct  means  of  determining  the  germ  count 
of  the  dirt  falling  from  the  udder  and  the  flank  of  the  cow  during  the 
milking  process  is  to  secure  some  of  this  material  and  to  determine 
the  germ  count  of  weighed  quantities  of  this  dry  dirt. 


19  HI] 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIRT 


385 


The  two  cows  used  in  making  this  test  were  in  two  different  barns. 
Cow  152  was  in  Barn  I.  She  had  been  brushed  daily  and  her  coat 
showed  no  visible  dirt.  She  was  representative  of  very  clean  cows. 
Cow  1039  was  in  Barn  III,  and  her  condition  and  surroundings  were 
the  same  as  the  seven  cows  in  Series  I  and  II.  Her  flank  and  abdomen 
were  partially  covered  with  dried  manure  and  she  was  an  extremely 
dirty  cow. 

Neither  cow  was  in  milk,  and  the  samples  were  collected  using  a 
sterilized,  open-top,  milk  pail.  Any  loose  bedding  on  the  flanks  or 
udder  was  brushed  away  by  hand,  as  is  customary  before  milking, 
but  the  cows  were  not  otherwise  prepared  for  the  tests.  The  pail  was 
held  partially  under  the  udder,  as  would  be  done  during  ordinary 
hand-milking,  and  the  udder  was  manipulated  as  tho  the  cow  were 
being  milked.  In  the  first  two  tests  the  manipulation  was  continued 
for  seven  minutes,  and  in  the  other  three,  for  ten  minutes.  The  pail 
was  then  taken  to  the  laboratory  and  the  visible  dirt  was  brushed  out 
and  weighed.  The  dirt  was  then  mixed  with  a  definite  amount  of 
sterile  skimmed  milk  and  after  being  mixed  for  fifteen  to  twenty-five 
minutes  plates  were  prepared  for  germ-count  determinations.  The 
results  of  five  such  determinations  are  given  in  Table  9. 

TABLE  9. — GERM  COUNT  OF  DIRT  FROM  COATS  OF  Cows 


No.  of  cow 

Condition 
of  cow 

Dirt  from 
milk  pail 

Germ  count 
of  dirt 

Germ  count 
per  1  gram 

152*... 

Clean  

gms. 
.043 

766  000 

17814000 

1039*  

Dirty.  . 

240 

94  285  000 

392  800  000 

j> 

» 

.108 

496  000  000 

4  592  000  000 

» 

» 

.083 

15  300  000 

184  300  000 

» 

» 

.171 

293  475  000 

1  716  000  000 

*  In.  these  two  tests  the  manipulation  of  the  udder  was  continued  but  seven 
minutes,  while  in  the  other  three  the  manipulation  lasted  ten  minutes.  To 
facilitate  comparison,  the  amount  of  dirt  and  its  germ  count  was  increased  to 
a  ten-minute  basis.  This  did  not  affect  the  final  computation  of  germ  count 
per  gram  of  dirt. 

From  Table  9  it  will  be  seen  that  clean  and  dirty  cows  are  in  dif- 
ferent classes,  both  in  the  amount  of  dirt  falling  into  the  pail  during  a 
given  time  and  in  the  germ  count  resulting  from  a  gram  of  dirt.  In 
other  words,  the  dirt  from  a  dirty  cow  is  not  only  more  abundant  than 
from  a  clean  cow,  but  it  is  also  a  different  kind  of  dirt  with  a  much 
higher  germ  count  per  gram. 

In  removing  the  dirt  from  the  pail  during  the  experiments  it  was 
noted  that  the  dirt  falling  from  Cow  152  consisted  of  some  hair  and 
fine  dandruff.  The  dirt  from  Cow  1039  was  made  up  of  considerable 
hair,  dandruff,  and  many  fine  particles  of  dirt,  presumably  in  part 
dried  manure.  Because  of  the  distinctly  different  germ  count  of  the 


386 


BULLETIN  No.  236 


[December, 


material  from  the  two  cows,  interest  is  at  present  centered  upon  the 
results  from  Cow  1039,  since  she  was  a  companion  cow  with  the  seven 
dirty  cows  in  Barn  III. 

It  will  be  noted  that  four  tests  of  this  cow  on  successive  days  gave 
widely  differing  results,  not  only  in  the  amount  of  dirt  collected,  but 
also  in  the  germ  count  per  gram  of  this  dirt.  While  variation  is  un- 
doubtedly due  in  part  to  the  varying  germ  count  of  the  different  kinds 
of  dirt  finding  their  way  into  the  pail,  it  is  also  due  in  part  to  the 
difficulty  of  getting  representative  samples  of  the  material  in  making 
the  plates.  In  preparing  the  samples  the  dirt  was  placed  in  measured 
amounts  of  milk  varying  from  500  cc.  to  5,000  cc.,  and  after  fifteen 
minutes  of  thoro  shaking  samples  were  taken  for  plating  within  the 
following  ten  minutes.  The  number  of  samples  taken,  from  which 
dilutions  and  plates  were  made,  varied  from  two  to  twenty  on  the 
different  days,  and  six  to  nine  plates  were  made  from  each  sample. 
Not  all  of  these  plates  could  be  counted,  but  the  germ  counts  given  for 
the  four  tests  of  Cow  1039  are  based  upon  counts  from  11,  20,  13,  and 
46  plates  respectively. 

Extreme  variations  occurred  in  connection  with  the  second  test  of 
Cow  1039,  and  as  this  was  the  test  giving  the  highest  germ  count  per 
gram,  and  as  the  results  well  illustrate  the  difficulties  in  determining 
the  germ  count  of  such  material,  they  will  be  given  in  some  detail.  In 
this  experiment  0.108  of  a  gram  of  dirt  was  suspended  in  500  cc.  of 
milk.  Four  separate  samples  were  drawn  from  this  suspension,  and 
nine  plates  were  made  from  each  sample.  The  results  are  given  in 
Table  10. 


TABLE  10. — GERM  COUNT  WITH  0.108  OP  A  GRAM  OP  DIRT  SUSPENDED  IN 

500  cc.  OF  MILK 


Sample 

Plates 
counted 

Average 
per  cc. 

Total  germs 
in  500  cc. 

Germ  count  per 
1  gram  of  dirt 

I.. 

6 

878  000 

439  000  000 

4  064  000  000 

II  •  

5 

611  000 

305  750  000 

2  831  000  000 

Ill  

3 

143  000 

71  500  000 

662  000  000 

IV  

6 

2  336  000 

1  168  000  000 

10  810  000  000 

Had  any  one  of  the  four  samples  shown  in  Table  10  been  taken 
alone,  the  germ  count  of  this  dirt  might  have  been  given  as  anything 
between  662  million  and  10,810  million  per  gram. 

An  inspection  of  the  records  of  the  plates  made  from  the  four 
samples  shows  that  the  plates  made  from  each  sample  agree  fairly 
well  among  themselves.  For  example,  in  Sample  III  the  three  plates 
made  from  the  1-1000  dilution  produced  127,  150  and  152  colonies 
respectively.  Likewise,  the  three  similar  plates  from  Sample  IV  pro- 
duced 1,800,  2,000,  and  2,050  colonies.  The  difficulty  in  getting  ac- 
cordant results  from  the  examination  of  such  suspensions  of  dirt  in 


1921]          GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIRT  387 

milk  seems  to  lie  principally  in  withdrawing  representative  samples. 
The  fact  that  in  these  experiments  the  dirt  was  suspended  in  less  than 
one-tenth  of  the  volume  of  milk  in  which  it  would  be  suspended  in 
ordinary  milking  undoubtedly  added  to  the  difficulty. 

Reverting  again  to  the  data  from  the  four  determinations  of  the 
germ  count  of  the  dirt  from  Cow  1039,  as  given  in  Table  9,  it  is  plain 
that  little  can  be  gained  by  considering  a  mathematical  average  of 
germ  counts  which  vary  from  184  million  to  4,592  million  per  gram. 
At  the  same  time  it  is  clear  that  if  a  large  number  of  such  determina- 
tions were  averaged,  as  was  done  with  each  of  the  three  series  of 
samples  from  Barn  III,  it  is  altogether  likely  that  such  an  average 
would  show  a  germ  count  for  the  dirt  of  at  least  1.5  billion  per  gram. 
Accordingly,  in  so  far  as  conclusions  can  be  drawn  from  such  a  lim- 
ited number  of  observations,  these  direct  examinations  of.  the  dirt  fall- 
ing into  the  milk  pail  from  a  dirty  cow  suggest  that  the  dirt  recovered 
from  the  milk  in  the  three  series  of  examinations  was  sufficient  in 
amount  to  account  for  the  increase  found  in  the  germ  count.  In  other 
words,  these  results  tend  to  show  that  the  methods  employed  in  recov- 
ering the  dirt  from  the  milk  recovered  essentially  all  of  the  dirt. 

In  the  case  of  three  of  the  suspensions  included  in  Table  9,  where 
a  known  amount  of  dirt  was  suspended  in  500  cc.  of  skim  milk,, 
advantage  was  taken  of  the  opportunity  to  test  the  extent  to  which 
it  was  possible  to  recover  this  dirt  by  nitration  thru  cotton.  In  each 
case  the  weight  of  the  cotton  filter,  after  filtration  and  drying,  was 
found  to  be  increased  by  an  amount  slightly  in  excess  of  the  weight 
of  the  dirt  added  to  the  milk.  Evidently  the  milk  adhering  ten- 
aciously to  the  cotton  more  than  offset  any  tendency  of  the  dirt  to 
go  into  the  solution,  or  to  pass  thru  the  cotton.  As  the  technic 
employed  in  the  case  of  these  500-cc.  suspensions  was  different  from 
that  employed  in  removing  the  dirt  from  the  large  quantities  of 
normal  milk,  they  throw  little  light  upon  the  accuracy  of  the  other 
method,  except  to  suggest  that  the  element  of  solubility  is  not  large 
in  the  case  of  the  dirt  which  falls  into  the  milk,  from  extremely  dirty 
cows. 


388  BULLETIN  No.  236  [December, 


SUMMARY  AND  CONCLUSIONS 

It  is  a  matter  of  common  knowledge  that  under  ordinary  dairy 
conditions  practically  all  the  dirt  entering  the  milk  at  the  farm  enters 
during  the  act  of  milking. 

The  use  of  the  small-topped  pail  materially  reduces  the  amount 
of  dirt  entering  the  milk,  the  reduction  varying  from  25  to  40  percent. 

The  quantity  of  dirt  entering  the  milk  during  the  milking  process 
is  small.  When  the  cows  were  unusually  dirty,  and  were  milked  into 
an  open-topped  pail,  the  dirt  in  the  unstrained  milk  amounted  to  10.8 
milligrams  per  quart.  When  the  conditions  were  comparable  to  those 
of  ordinary  dairies,  and  the  small-topped  pail  was  used,  the  dirt  in 
the  milk  was  less  than  5  milligrams  per  quart.  Under  conditions 
comparable  with  the  better  class  of  market  milk  dairies,  and  when  the 
small-topped  pail  was  used,  the  proportion  of  dirt  was  about  2.5  milli- 
grams per  quart. 

The  kinds  of  dirt  falling  into  the  milk  vary  with  the  condition  of 
the  coat  of  the  cow.  With  hand-milking,  the  entrance  of  some  hair 
and  dandruff  is  practically  unavoidable,  tho  the  amount  may  be 
•reduced  by  regularly  brushing  the  coat  of  the  cow.  If  the  flank  or 
udder  is  soiled  with  dried  manure  and  other  dirt,  some  of  this  may 
find  its  way  into  the  milk. 

Thoro  straining  removes  the  hair,  dandruff,  and  larger  particles 
which  form  75  to  90  percent  of  the  dirt. 

While  some  of  the  dirt  undoubtedly  passes  into  solution  in  the 
milk,  the  amount  in  this  study  was  so  small  that  it  escaped  deter- 
mination. 

Germ  life  is  abundant  on  the  dirt  from  extremely  dirty  cows,  the 
plate  counts  indicating  approximately  1.5  billion  per  gram  of  dirt. 
However,  owing  to  the  small  amount  of  this  dirt  which  finds  its  way 
into  milk,  the  effect  of  the  dirt  upon  the  germ  count  of  the  milk  is 
relatively  small.  When  the  cows  were  extremely  dirty,  and  the  dirt 
in  the  milk  amounted  to  10.8  milligrams  per  quart,  the  increase  in 
the  germ  count  of  the  milk,  due  to  dirt,  was  about  17,000  per  cc. 
Under  the  same  conditions,  except  that  the  use  of  the  small-topped  pail 
reduced  the  dirt  entering  the  milk  to  8.1  milligrams  per  quart,  the 
germ  count  due  to  dirt  fell  to  13,000  per  cc. 

In  ordinary  milk  production,  germ  counts  as  low  as  17,000  per  cc. 
resulting  from  any  factor  will  be  entirely  overshadowed  by  the  influ- 
ence of  utensils  and  other  factors.  Where  the  time  interval  permits 
growth,  any  attempt  to  judge  of  the  conditions  of  cleanliness  sur- 
rounding the  production  of  a  given  sample  of  milk,  on  the  basis  of 
its  germ  count,  becomes  hopeless. 


1921}          GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIET  389 


,miu 

RELATION  OF  THESE  RESULTS  TO  THE  PROBLEM 
OF  CLEAN  MILK 

When  the  results  of  this  study  are  properly  understood,  it  will 
be  clear  that  they  cannot  be  used  legitimately  as  an  excuse  for  the 
production  of  dirty  milk. 

The  study  shows  that  where  the  germ  count  is  relied  upon  to  pro- 
tect the  consumer  against  milk  which  has  contained  a  relatively  large 
amount  of  visible  dirt,  the  consumer  will  not  be  protected.  It  is 
entirely  possible  for  the  dirtiest  milk  to  pass  the  most  stringent 
standards,  based  on  bacterial  counts,  which  have  been  established  in 
connection  with  the  supervision  of  municipal  milk  supplies. 

While  it  is  still  an  open  question  as  to  what  may  ultimately  be 
accepted  as  the  most  satisfactory  index  for  the  keeping  quality  of 
milk,  there  is  no  question  but  that  when  the  bacterial  count  is  prop- 
erly determined  it  is  a  serviceable  index  for  this  purpose.  It  is  not, 
however,  an  index  by  which  the  presence  of  dirt  can  be  determined, 
for  the  bacteria  are  commonly  so  numerous  in  milk,  and  come  from 
so  many  sources  other  than  dirt,  that  there  is  no  constant  relation 
between  the  dirt  content  and  the  number  of  germs  present.  Such 
being  the  case,  the  conclusive  demonstration  of  the  uselessness  of 
bacterial  counts  as  a  means  of  detecting  the  presence  of  dirt  is  the 
necessary  first  step  toward  developing  methods  for  accurately  safe- 
guarding the  public  against  dirty  milk. 

As  has  been  repeatedly  pointed  out  in  this  publication,  if  the  public 
is  to  be  protected  against  dirty  milk  it  must  be,  not  thru  attention  to 
germ  counts,  useful  as  germ  counts  are  as  a  measure  of  keeping  qual- 
ity, but  thru  attention  to  measurements  of  the  dirt  actually  present. 

The  measurements  herein  reported  are  submitted  as  a  pioneer 
attempt  looking  toward  the  formulation  of  better  standards  for  clean 
milk. 


390  BULLETIN  No.  236 

EEFEEENCES 

1.  HARDING,  H.  A.,  BREED,  E.  S.,  STOCKING,  W.  A.  JR.,  AND  HASTINGS,  E*.  G. 
What  is  meant  by  "quality"  in  milk.    111.  Agr.  Exp.  Sta.  Cire.  205.    1917. 

2.  VON  EENK,  PROF.     Uber  die  Marktmilch  in  Halle  a/S.     Miinchener  Med. 
Wochenschr,  38,  99-102,  131-132.    1891. 

3.  PRYLEWSKI.     Versuchemit  einem  Apparat  zur  Priifung  des  Schmutzgehaltes 
der  Milch,  genannt,  ' '  Patent  Fliegel ' '  Molkerei-Zeit.,  14,  541.    1904. 

4.  BERNSTEIN,   ALEX.     Ein    Schmutzprober   fiir    Milch.   Zeit.    f.    Fleisch   und 
Milchhyg.,  16,  264-265.     1906. 

5.  WELD,  I.  C.    A  plan  for  improving  the  quality  of  milk  and  cream  furnished 
to  New  Hampshire  creameries.     N.  H.  Agr.  Exp.  Sta.  Bui.  132.     1907. 

6.  BABCOCK,  S.  M.,  AND  FARRINGTON,  E.  H.    New  and  improved  tests  of  dairy 
products.    Wis.  Agr.  Bxp.  Sta.  Bui.  195.    1910. 

7.  MUNICIPAL  LABORATORY.    Dept.  of  Health,  City  of  Chicago.    Eeport  for  1907- 
1910,  p.  25. 

8.  Third  report  of  the  Committee  on  Standard  Methods  for  the  Sanitary  Analysis 
of  Milk.     Adopted  by  the  Laboratory  Section  A.  P.  H.  A.     San  Francisco, 
Sept.  1920. 

9.  EICHLOFF,  E.     Ueber  die  Bestimmung  des  Schmutzgehaltes  in  Milch.  Zeit- 
schr.  f.  Untersuch.  d.  Nahr.  u.  Genussmtl.,  1,  678-683.     1898. 

10.  STOCKING,  W.  A.  JR.    The  covered  pail  a  factor  in  sanitary  milk  production. 
Storrs  (Conn.)  Agr.  Exp.  Sta.  Bui.  25.  1903. 

11.  Feeding  green  feed  before  and  dry  feed  after  milking  was  a  regulation  of  the 
Willowbank  Dairy  in  Glascow  about  1809.     Martiny  B.  Vor  hundert  Jahren. 
Leipsic.     1904. 

12.  PRUCHA,  M.  J.,  WEETER,  H.  M.,  AND  CHAMBERS,  W.  H.     Germ  content  of 
milk:    II.  As  influenced  by  the  utensils.    111.  Agr.  Exp.  Sta.  Bui.  204.     1918. 

13.  See  10,  above. 

14.  EUEHLE,  G.  L.  A.,  AND  KULP,  W.  L.     Germ  content  of  stable  air  and  its 
effect  upon  the  germ  content  of  milk.    N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui. 
409,  418-474.     1915. 

15.  Compare,  for  example,  the  number  of  dust  particles  per  cubic  foot  of  air  as 
reported  on  page  61  of  Final  Eeport  of  the  Committee  on  Standard  Methods 
for  the  Examination  of  Air  (Am.  Jour.  Pub.  Health,  7,  54-72,  1917),  where 
the  number  of  dust  particles  per  cubic  foot  of  the  air  of  New  York  City 
streets  is   given   as  between  400,000   and    1,000,000   as  determined  by  the 
filtration  method, — with  the  number  of  bacteria  per  cubic  foot  of  air  as  re- 
ported by  Winslow,  C.  E.  A.,  and  Browne,  W.  W.     (The  microbic  content  of 
indoor  and  outdoor  air,  Monthly  Weather  Eeview,  42,  452-453,  1914).     The 
average  numbers  of  bacteria  which  the  latter  authors  report  do  not  exceed 
113  per  cubic  foot  for  air  from  the  open  country,  from  city  streets,  from 
offices,  from  factories,  and  from  schools. 

16.  GROSSE-BOHLE,  H.     Die  hygienische  uberwachung  des  Verkehrs  mit  Milch. 
Zeit.  f.  Untersuchung  d.  Nahr.  u.  Genussmtl.,  14,  78-89.     1907. 

17.  See  7,  above. 

18.  PRUCHA,  M.  J.,  AND  WEETER,  H.  M.    Germ  content  of  milk :    I.  As  influenced 
by  the  factors  at  the  barn.    111.  Agr.  Exp.  Sta.  Bui.  199.     1917. 

19.  HARDING,  H.  A.,  AND  WILSON,  J.  K.    A  Study  of  the  udder  flora  of  cows. 
N.  Y.   (Geneva)   Agr.  Exp.  Sta.     Tech.  Bui.  27.     1913. 

20.  See  8,  above. 


1921} 


GERM  CONTENT  OF  MILK  AS  INFLUENCED  BY  VISIBLE  DIET 


391 


Cow  1033 

The  coat  of  Cow  1033  is  shown  as  typical  of  the  condition  of 
the  dirty  cows  during  the  experiments  reported  on  pages  375-380. 
The  germ  count  of  the  milk  from  these  cows  was  increased  17,000 
per  cc.  by  the  dirt  which  fell  into  it  during  the  process  of  milking, 
when  the  cows  were  milked  into  open-topped  pails.  When  small- 
topped  pails  were  used,  the  germ  count  of  the  milk  was  increased 
13,000  per  cc.  by  the  dirt  falling  into  it. 


UMA 


UNIVERSITY  OF  ILLINOIS-URBANA 


